Post-Tech® Corrosion Evaluation
Post-Tech® Corrosion Evaluation
As part of an overall condition assessment of post-tensioned structures, a Post-Tech® Corrosion Evaluation can determine the cause and extent of corrosion risk and assist owners and engineers in preparating an effective and economical corrosion mitigation strategy.
Post-Tech® Corrosion Evaluation is a non-destructive test method that determines the degree of wetness inside a post-tensioned cable sheath by injecting a dry gas and measuring the moisture content in the exhaust from the venting ports. This test can be conducted on a subset of cables as pilot sample before commissioning a complete full-scale evaluation of all cables.
Post-Tech® Cable Break Detection utilizes a magnetic field to detect cable breaks and defects in post-tensioned and prestressed concrete structures. After the cables are magnetized, breaks are detected with sensors and state-of-art software.
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Evaluation Process
- A central test pit, located on the underside of the slab is often used in Full-Scale testing. This serves well for visual inspection and future corrosion mitigation.
- Two small holes (approx. 5/8in (16 mm) diameter) are drilled into the structure to access the post-tensioned strand's sheath near the end anchorages.
- Air ports are inserted and secured.
- Dry gas is injected at low pressure through the cable sheath.
- Measurements of the relative humidity and temperature of the air escaping from each of the “out” ports are taken using a calibrated Relative Humidity & Temperature (RH & T) sensor.
- The degree of wetness of each strand is assessed by grading the moisture content of the escaping air using the Post-Tech three-point system.
Research has demonstrated excellent correlation between the Post-Tech® Corrosion Evaluation grade and the observed corrosion on cables removed for inspection. If a site-specific correlation is required, a small percentage of tendons which are representative of the different construction pours and moisture levels within the structure, can be removed and inspected.
Results
The Post-Tech® Corrosion Evaluation results are depicted both graphically and on color-coded drawings. Each section of cable tested is color-coded to indicate the probable corrosion condition. This system permits ready evaluation of the test results for individual cables, for select areas of the structure, and for the structure as a whole. Permanent identification of all cables in a structure facilitates future inspection, repair, and preventative maintenance.
Once the Post-Tech® Corrosion Evaluation has determined the potential for corrosion, a mitigation plan can be put into place using the Post-Tech PT Cable Drying system and PT Grease Injection to extend the service life and integrity of post-tensioned structures at a fraction of the cost of other repair methods.
The Post-Tech® range of corrosion solutions is used as part of an overall strategy for the evaluation, identification, and protection of post-tensioned concrete structures. Structural assessments should be conducted by a qualified structural engineer.
Applications
- Unbonded post-tensioned slabs or beams in parking structures
- Unbonded post-tensioned building slabs
Technical Documents
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